Doppler radar is a type of radar system that uses electromagnetic waves to determine radial velocity of a target at a distance from an observer (speed toward/away from an observer), and it has a number of uses including determining the rate of descent of aircraft, the speed of moving objects and the like. A Doppler radar unit generally transmits an electromagnetic wave (sometimes referred to as a radar signal) that reflects off a target and returns to the radar unit. Movement of the target in a radial direction relative to the radar unit causes a change in the frequency of the reflected signal relative to the transmitted signal, often referred to as the Doppler effect (or Doppler shift). More specifically, the radial movement of the target changes the frequency of the radar signal an amount that is proportional to the relative velocity of the target such that the change in frequency of the radar signal may be used to determine the location and speed of the moving target.
A number of techniques have been developed to calibrate and certify Doppler radar units, most notably those involving use of a vibrating tuning fork. According to this technique, the tuning fork produces a signal representing that caused by reflection of a radar signal by a target (i.e., the tuning fork produces a signal representing a reflected signal), and which has a known relationship to an expected speed of the target. The radar unit responds to the signal by calculating a speed, which may be compared to the expected speed to determine the accuracy of the radar unit. And from this comparison, the radar unit may be calibrated or otherwise certified for use.
Although the existing tuning fork technique is adequate, it has drawbacks. The current tuning fork technique process generally only tests a single point, namely the single frequency of the signal produced by the tuning fork. The tuning fork itself may also be prone to changes do to temperature and physical damage due to striking the fork too hard on a solid surface. Other existing techniques include use of a vehicle and stationary reflector or a moving object, but these techniques are generally less accurate and stable. These and other similar existing techniques are also typically inadequate for calculating very low speeds, particularly in the case of rates of descent.
Therefore, it may be desirable to have a system and method that takes into account at least some of the issues discussed above, as well as possibly other issues.